[core] Responses to NON with 4.02

Christian Amsüss <christian@amsuess.com> Tue, 16 February 2021 20:29 UTC

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Subject: [core] Responses to NON with 4.02
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Hi,

reviewing new-block told me something new about RFC7252, that is that a
response to a NON request containing an unknown critical option MUST be
either RST or complete silence (whereas in the CON case, 4.02 is the
logical response).

Why is that? A NON 4.02 response would be just the same size, give
better information, and (to me, most importantly) would not require the
additional case distinction between "it's a 4.02 because some option
value doesn't make sense" and "it's a 4.02 because I don't know the
particular option" at a very different place than were the options are
understood.

(Or worse yet: A NON may arrive at a proxy that forwards it over TCP or
as a CON, and by the time the proxy gets the 4.02, it doesn't know
either).

And will anything go Really Bad if I ignore that MUST? (I currently do
-- up to now for ignorance, going forward because my libraries all work
under the fiction that the library is an intermediary, and thus may do
all things an intermediary may do).

BR
c

-- 
To use raw power is to make yourself infinitely vulnerable to greater powers.
  -- Bene Gesserit axiom